1. Field of the Invention
The present invention relates to a control device of a permanent magnet synchronous electric motor (hereinafter referred to simply as “permanent magnet motor”), which creates a magnetic pole phase signal of a rotor based on a rotation phase signal, obtained by detecting the rotation of the output axis of the permanent magnet motor, and synchronously controls the permanent magnet motor in compliance with the magnetic pole phase signal.
2. Description of the Related Art
FIG. 7 is a block diagram showing the constitution of a control device of a permanent magnet motor which drives, for example, an elevator. In FIG. 7, a rotation position detector 2 is connected to an electric motor 1. The rotation position detector 2 detects the rotation position of the electric motor 1, and outputs, for example, a rotation phase signal φh permanent magnet motor having a number of signal repeats of two during one rotation of the motor, the rotation phase signal φ being applied to a magnetic pole phase converter 3. The magnetic pole phase converter 3 converts the rotation phase signal φ to a magnetic pole phase signal θ having a rotation number corresponding to the magnetic pole logarithm, and applies this to an electric motor controller 4. The electric motor controller 4 controls the current of a stator so that it generates a magnetic field in synchronism with the magnetic pole phase signal.
In this case, the magnetic pole phase converter 3 uses the value obtained by dividing the magnetic pole logarithm of the electric motor 1 by the number of signal repeats in one rotation of the rotation position detector 2 as a conversion coefficient, multiplies the rotation phase signal φ by the conversion coefficient, and creates the magnetic pole phase signal θ by taking the remainder after dividing the obtained signal by the rotation angle for one rotation (e.g. 360 degrees). By this method, the electric motor 1 is synchronously controlled.
However, in the conventional method for creating the magnetic pole phase signal described above, unless the magnetic pole logarithm of the electric motor 1 is an integral multiple of the number of repeats of the signal output from the rotation position detector 2, the position of the magnetic pole cannot be detected accurately and it becomes impossible to control the synchrony. This point will be explained using FIGS. 8 and 9.
For example, when the magnetic pole logarithm of the electric motor 1 is four and the number of repeats of the rotation phase signal output by the rotation position detector 2 during one rotation of the electric motor 1 is two, the value of the rotation phase signal φ of the rotation position detector 2 changes in a saw-tooth shape twice during one actual rotation of the motor, as shown in FIG. 8A. In contrast, when the magnetic pole logarithm of the electric motor 1 is four, the magnetic pole phase signal changes in a saw-tooth shape four times during one actual rotation of the motor, as shown in FIG. 8B. Since the number of repeats of the rotation phase signal φ is two and the magnetic pole logarithm is four, the magnetic pole phase converter 3 multiplies the rotation phase signal φ by a conversion coefficient of 4/2=2, and outputs the remainder obtained by sequentially dividing by 360 degrees, i.e. a magnetic pole phase signal increasing from zero degrees to 360 degrees four times during one rotation of the motor. Consequently, the signal shown in FIG. 8B is obtained, enabling the system shown in FIG. 7 to control the synchrony of the electric motor 1.
On the other hand, when the magnetic pole logarithm of the electric motor 1 is three and the number of repeats of the rotation phase signal output by the rotation position detector 2 during one rotation of the electric motor 1 is two, the value of the rotation phase signal φ of the rotation position detector 2 changes in a saw-tooth shape twice, as shown in FIG. 9A. When the magnetic pole phase converter 3 divides the magnetic pole logarithm (three) by the number of signal repeats of the rotation position detector 2 (two), the conversion coefficient becomes 3/2. When the magnetic pole phase converter 3 multiplies this conversion coefficient of 3/2 by the value of the rotation position detection phase, and outputs the value of the remainder obtained by subtracting 360 degrees as the magnetic pole phase signal, as shown in FIG. 9B, the magnetic pole phase becomes discontinuous, rising from zero degrees to 360 degrees as the angle of rotation of the motor increases from zero degrees to 120 degrees, rising from zero degrees to 180 degrees as the angle of rotation of the motor increases from 120 degrees to 180 degrees, and then repeating the same change as the angle of rotation of the motor increases from 180 degrees to 360 degrees. For this reason, the system shown in FIG. 7 is incapable of controlling the electric motor 1 in synchronism with the magnetic pole logarithm.